1. Field of the Invention
This invention relates to a device for controlling a focal plane electric shutter, and more particularly to a device for controlling the timing of the start of the shutter curtains of an electrically controlled focal plane shutter.
2. Description of the Prior Art
Various types of electric shutters have heretofore been proposed and developed. In a focal plane shutter, the shutter speed or the exposure time is usually controlled by controlling by an electromagnetic means the timing of the start of the trailing curtain after the start of the leading curtain. The period of the delay from the start of the leading curtain to the start of the trailing curtain is normally controlled by use of the time constant of an RC circuit which includes a photodetector. The RC circuit is connected with an electromagnet which releases a holding means which holds the trailing curtain.
In such a type of electric focal plane shutter, a difficulty arises when a selftimer is used on the camera. When a selftimer is used simply in a mechanical or electrical connection with a shutter release member in the camera, the electromagnet to be operated to release the trailing curtain is excited from the start of the operation of the selftimer, which results in a waste consumption of the cell loaded in the camera. In the conventional electric focal plane shutter, the control of the shutter speed becomes impossible when the voltage of the cell is lowered beyond a predetermined level.